^it would cause more turbulence with more blades, and more noise, and more power use and...

These fans are designed for airflow, not pressure, hence the very steep angle, but low surface area of the fins. Ideally you would be using them at 500-600RPM at most, and they still push very respectable air. A P12 at the same speed would be less efficient.

I ended up getting three of the Medium speed 9S1212M4011s .13Amp 1850rpm and two Low speed 9S1212L4011s .08Amp 1500rpm for front intake. They don't come with any of the niceties like the Noctua fans splitters and extension cables and voltage attenuators, they just arrive like this nothing fancy at all:

So you have to add connectors to the ends and sleeve them. I got the standard voltage driven fans to use with a Lamptron FC-5V2 controller, but Sanyo Denki also makes a PWM version, I just could not find it anywhere in the US.

They are a bit industrial looking and cost more than the Noctua NF-F12s after tax and shipping and sleeving, but they are more decibel efficient than the NF-F12s or any fan I have used so far.